Leonardo’s Mountain of Clams and the Diet of Worms Page 10
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DARWIN’S AMERICAN SOULMATE: A BIRD’S-EYE VIEW
I HAVE LONG CONSIDERED ABRAHAM LINCOLN AS CHARLES DARWIN’S American soulmate—for they were born on the same day, February 12, 1809. But perhaps the accidents of joint beginnings should not define a concept of such intimacy. If soulmates must be linked more tightly by their active choices, then Darwin’s American alter ego can only be his fellow scientist James Dwight Dana (1813–1895)—geologist, biologist, longtime professor at Yale, and surely America’s preeminent indigenous natural historian of the nineteenth century. (Louis Agassiz, the other obvious contender, was born in Switzerland and did his important scientific work in Europe before coming to Harvard University in the late 1840s.)
Dana and Darwin never met personally—though they both expressed a warm desire to do so in their numerous letters. But their careers and interests ran in intricate, almost eerily parallel courses. Both men had their scientific baptism in a long sea voyage around the world—Darwin on the Beagle from 1831 to 1836, and Dana on the Wilkes expedition of 1838–1842, young America’s greatest international scientific journey, dispatched primarily to assess whaling prospects in the southern oceans. Both men, similarly inspired by their travels, then built their scientific careers on the same two subjects.
Darwin’s first scientific book, published in 1842, presented a correct theory on the origin of coral atolls by subsidence of a central island, with continued upgrowth of living coral at the edges. Dana also became fascinated with corals when he visited Pacific reefs. In 1839, while ashore in Sydney, Dana chanced upon a description of Darwin’s ideas in a local newspaper. With this inspiration, Dana produced the other great nineteenth-century work on coral reefs—Corals and Coral Islands—substantially supporting Darwin’s “subsidence theory,” but based on far more extensive observation than Darwin had been able to make. In the preface to the second edition of his book on coral reefs, Darwin wrote:
The first edition of this book appeared in 1842, and since then only one important work on the same subject has appeared, namely . . . by Professor Dana . . . It has also afforded me the highest satisfaction to find that he accepts the fundamental proposition that lagoon-islands or atolls, and barrier-reefs, have been formed during periods of subsidence.
In a second parallel, both Darwin and Dana devoted their major technical work in zoology to the taxonomy of the same group of organisms—the crustacean arthropods. Darwin published four volumes between 1851 and 1854 on the oddest of crustacea, the barnacles. Dana based fourteen years of research on specimens collected by the Wilkes expedition, and published his finest work in 1852—two volumes on the taxonomy of crustaceans.
In fact, Darwin’s barnacles inspired the first personal contact between the two men in 1849, when Darwin wrote to ask if he might borrow specimens collected by Dana’s expedition. (Thus, the striking similarity of their careers had developed without any direct mutual encouragement.) Darwin wrote, rather formally:
I hope that you will forgive the liberty I take in addressing you . . . in order to beg, if it lies in your power, assistance . . . It is my earnest wish to make my monograph as perfect as I can. Can you lend me any species collected during your great expedition?
Dana replied, warmly but sadly, that he would be personally delighted to do so, but had neither possession nor authority over the specimens. Darwin understood, and wrote Dana a long letter of praise for his work, noting: “You cannot imagine how much gratified I have been that you have to a certain extent agreed with my coral island notions.”
A warm epistolary friendship ensued. Darwin wrote three years later, in 1852:
You ask whether I shall ever come to the United States. I can assure you that no tour whatever could be half so interesting to me, but with my large family I do not suppose that I shall ever leave home. It would be a real pleasure for me to make your personal acquaintance.
(Darwin knew himself well. After sailing around the world and returning to England, he never again left his island home; he never even crossed the English Channel!)
The next year, Darwin enthused over Dana’s volumes on crustacea, just published:
If you had done nothing else whatever, it would have been a magnum opus for life. Forgive my presuming to estimate your labors, but when I think that this work has followed your Corals and your Geology, I am really lost in astonishment at what you have done in mental labor. And then, besides the labor, so much originality in all your works!
Despite this effusion of warmth and mutual support, Dana and Darwin inevitably parted company on the great issue that would define their time (and ours)—evolution itself. As I shall document later, Dana did eventually succumb to the inevitable in the mid-1870s, but his late support for evolution always remained strictly limited, clearly grudging, and only pursued as a necessary compromise to save as much as possible of his unaltered worldview. But Dana remained a staunch, if always cordial, opponent of evolution throughout the great debates of the 1860s, the defining decade after Darwin published the Origin of Species in 1859.
Darwin sent Dana a copy of the first edition, but Dana’s health had broken, and he did not read the book until 1863. Nonetheless, Dana could not avoid the issue in publishing the first edition of his most famous work in 1862—the Manual of Geology. While stating his opposition in the book, Dana also thought that he owed his epistolary friend a personal explanation. So he wrote to Darwin on February 5, 1863: “I hope that ere this you have the copy of the Geology (and without any charge of expense, as was my intention). I have still to report your book unread; for my head has all it can now do in my college duties.”
Dana then spelled out his major objections, all paleontological, in a series of three points. Dana’s arguments show that he based his opposition upon his personal definition of evolution as a necessarily progressive and gradual process. If evolution were valid, Dana claimed, then the history of life would have to proceed by slow and steady transformation from simple to complex forms in each lineage. Dana then listed his objections:
1. The absence, in the great majority of cases, of those transitions by small differences required by such a theory . . .
2. The fact of the commencement of types in some cases by their higher groups of species instead of the lower . . .
3. The fact that with the transitions in the strata and formations, the exterminations of species often cut the threads of genera, families, and tribes . . . and yet the threads have been started again in new species.
Dana had cited a set of highly traditional objections—lack of transitional forms, first geological appearance of advanced rather than primitive members of a lineage, and mass extinctions—and Darwin rebutted them all (not entirely successfully, as later history would show) by arguing that a woefully imperfect fossil record had rendered a truly gradual and progressive history of life in this deceptive manner. Darwin did feel that he owed Dana a personal reply, and he wrote back with his usual rationale on February 20, 1863—just two weeks after Dana had dated his letter, and not bad for sea transport of mail during the Civil War:
With respect to the change of species, I fully admit your objections are perfectly valid. I have noticed them . . . I admit the same if the geological record is not excessively imperfect.
Then, in the only hint of rancor that I have ever detected in their correspondence, Darwin upbraids Dana for stating these objections without reading his book—though he quickly falls back into his usual geniality, and also assures his friend that he only felt aggrieved because Dana’s opinion carried so much weight:
As my book has been lately somewhat attended to [lovely British understatement], perhaps it would have been better if, when you condemned all such views, you had stated that you had not been able yet to read it. But pray do not suppose that I think for one instant that, with your strong and slowly acquired convictions and immense knowledge, you could have been converted. The utmost that I could have hoped would have been that you might possibly have been here or
there staggered.
The personal and intellectual drama of Darwin and Dana provides the main subject for this essay, but I also write to illustrate a broader theme in the lives of scholars and the nature of science: the integrative power of worldviews (the positive side), and their hold as conceptual locks upon major innovation (the negative side). I will argue that Dana was not benighted, stupid, or particularly stubborn. Rather, he maintained a consistent, well-articulated, and clearly coherent theory of God and life—a worldview that just didn’t contain any logical space for a Darwinian concept of naturalistic evolution. One does not (and probably should not) surrender the system of a lifetime for one apparently errant bit of information. If we can do so at all, we will surrender such sources of succor and consistency with the same feelings that we experience when we leave a natal home or a first great love—slowly, sadly, prayerfully, and, above all, with deep affection and respect.
The issue of when to hold firm as suggestions of factual collapse accumulate, and when to plunge with abandon into the breach, defines the most interesting and important dilemma of intellectual autobiography—for this decision defines the borderline between competence and genius, or between sensibility and crankiness. In some crucial sense, the geniuses of history are people who know when to plunge and how to create the instruments of successful assault and replacement. But we must also remember that probably 99 percent of personal plunges fling potential heroes into whirlpools of error and erasure from history. Still, the message of these failures should not inspire calls for sticking with the tried and true at all costs—or else the earth would still occupy the center of a small universe, and people would still be the manufactured incarnations of a divinely ordained perfection. Most people, including the most polished intellectuals of every generation, never dare to take the plunge. This phenomenon of psychology and society produced the old cliché, usually attributed to the nineteenth-century German physicist Ernst Mach, that new theories only triumph fully when the old guard dies off.
Dana’s conservative, and ultimately superseded, worldview rested upon two central convictions that made Darwinian evolution impossible (not so much factually wrong as literally inconceivable within such a system). First, Dana was as pure a Platonist as nineteenth-century biology ever produced. He based his zoological ideas firmly on the old concept of “type”—an idealized form for each group of animals, with variation among individuals of a species as accidental departures from ideal propriety, and variation among species as organized sequences obeying “laws of form” that expressed the thoughts and plans of divinity. (Agassiz, Dana’s equally Platonic colleague, declared taxonomy to be the highest science, for each species represents a divine idea made flesh, and the arrangement of species therefore expresses the structure of divine thought. By understanding the system of order among species, we therefore achieve our closest insight into the character of God’s mind.)
Second, Dana viewed the entire geological history of the earth and life as one long, coherent, and heroic story with a moral—a tale of inexorable progress, expressed in both physical and biological history, and leading, inevitably and purposefully, to God’s final goal of a species imbued with sufficient consciousness to glorify His name and works. The physical earth, according to Dana, developed through time with the same gradualistic progress that defined life’s history. By following three major trends—the emergence of more and more land from the sea, the purification of the atmosphere, and progressive global cooling with consequent increase in climatic diversity by formation of zones from poles to tropics—the earth became more and more suited to the successively higher forms of life that God created in each new episode of progress. For inhabitants of the land must be ranked “higher” than denizens of the sea; pure air inspires healthy complexity (slithering reptiles in murky swamps versus sinewy mammals on the bright plains); and cooler climates require such advances as warm-blooded metabolism. Dana wrote in his Manual of Geology:
Thus the prevalence of waters involved inferiority of species. The increase of land, the gradual purification of the atmosphere, and the cooling of the globe, prepared the way for the higher species.
Lest anyone be tempted to read the sequence of successive creations, each with increasing excellence, in an evolutionary manner à la Darwin, Dana always took pains to state that such a history could only record the direct actions of a loving God with a goal in mind. Dana wrote in 1856:
The whole plan of creation had evident reference to Man as the end and crown of the animal kingdom, and to the present cool condition of the globe as, therefore, its most exalted state. It is hence obvious, that progression in the earth from a warmer to a cooler condition, necessarily involved progression from the lower to the higher races . . . The earlier races were of lower types, not because the Creative Hand was weak, but for the reason that the times, that is the temperature and condition of the globe, were just fitted, in each case, for the races produced, and the progress of the plan of creation, correspondingly, required it . . . The development of the plan of creation . . . was in accordance with the law of . . . progress from the simple to the complex, from comprehensive unity to multiplicity through successive individualizations.
Dana buttressed each of his two controlling ideas with a definite biological theory of his own construction. In attempting to explain why and how the history of life should feature a vector of progress as the fundamental thrust of created change through time, Dana invented an influential notion that he named “cephalization,” or increasing domination of the head. Crustaceans are segmented animals, and their classification largely depends upon the form and number of appendages on the head segments. (In ancestral arthropods, each body segment presumably bore a pair of legs. In later evolution, these appendages often become concentrated and specialized. Many paired organs of crustaceans and other modern arthropods—antennae, mouthparts, swimming paddles, claspers used as external genitalia—evolved from modified legs. Insect and crustacean mouthparts, especially when greatly magnified in TV nature specials, look particularly weird and, to use the modern vernacular, yucky, because we correctly perceive them as a bunch of little legs waving about—and legs just don’t protrude from mouths on a “proper” vertebrate model!) Dana, under the controlling influence of his progressivist worldview, therefore chose to arrange the diversity of modern crustaceans in sequences of primitive to advanced, as defined by complexity and domination of the head and its appendages. He then extended this principle of “cephalization” to all of animal life.
Dana first published his theory of cephalization in the mid-1850s, before learning about Darwin’s ideas. But he wrote his four major articles on the subject between 1863 and 1866 (all published in the American Journal of Science, a periodical that he edited).
I find the theory of cephalization wonderfully fascinating and a bit mad. If I could write a volume, rather than an essay, on this subject, I would gladly discuss each of Dana’s sixteen criteria (many with several subdivisions) for the supposedly objective measure of precise degrees in organic “highness” and “lowness” based on the character of the head and its relative domination of the body. I would also demonstrate the self-serving (for his worldview, not his persona) and “fluid” nature of these criteria—scarcely objective in any reasonable sense, but obviously constructed in order to validate Dana’s a priori desires, and almost wantonly fudged or changed whenever an apparent exception arose.
For example, one criterion states that progress can be measured by position of the head and brain along the body axis—the farther forward the better. Thus, Dana regards whales as “low” mammals because they have so much mouth and snout in front of the brain. But as soon as he gets stuck because a group he wants to regard as primitive happens to place a brain right up front, he just shifts his criteria. For example, he wants to place millipedes and centipedes below insects, but these many-legged arthropods situate their head and brain right at the front end. So he pronounces this particular head as weak, although
located in the “right” place—as measured by minimal domination over the rest of the body because “lowly” legs proliferate behind. Dana writes: “The head is here strictly at the anterior extremity; but the cephalic force has so feeble control, that the joints multiply behind.” Dana even admits, in several passages, that his criteria may be inconsistent, but he then argues that such complexity requires ever more subtle interpretations, and ever more experienced interpreters, to make the system work!
Each of Dana’s papers attempts a summary definition of cephalization as the dominant motor of life’s progressive history. His “last fling” on the subject, a final article in 1876 after a ten-year hiatus, offers this account:
In the low, there is, usually, large size and strength behind, an elongation of the whole structure, and a low degree of compactness in the parts before and behind; in the high, there is a relatively shorter and more compacted structure, a more forward distribution of the muscular forces or arrangements, and a better head; and the progress in grade . . . is progress along lines from the former condition toward the latter, that is, progress in the strength, perfection and dominance of the anterior or cephalic extremity; in a word, it is progress in cephalization.
Although Dana may have developed this concept of cephalization from his work on crustacea, and although he claimed an objective status for his theory, any thorough reading will reveal that he cobbled his theory together in order to proclaim the message that controlled his worldview: the centrality and domination of human life in the cosmos. Why choose cephalization as the criterion of progress, except as a way of exalting our own big head, located right at the top, with anterior limbs freed from the lowly task of locomotion and dedicated instead to the head’s service (as I type this essay with my fingers, but only curl my toes uselessly under my chair)? Dana wrote: